In internal combustion engines, the intake and exhaust valves are actuated by a cam or rocker pushing against the end of the valve stem, which then slides through the valve guide. The valve head at the end of the valve stem then clears its seat and opens the passage between the intake or exhaust passageway and the combustion chamber, allowing gases to enter or exit the chamber. The valve is forced to follow the motion of the cam or rocker by a valve spring, which may actually consist of several springs of varying diameter, with the inner spring(s) lying within the coils of another spring. The valve spring sits in a state of compression between the valve spring seat, which is mounted on the cylinder head and is therefore stationary, and the valve spring top collar, which is affixed to the end of the moving valve stem. The spring force is thereby transmitted to the valve stem, which is thus forced against the cam or rocker as the cam or rocker rises, causing the valve to close. A common conventional valve spring top collar resembles a solid disk with a central opening to admit the valve stem and a raised shoulder (or shoulders) on its underside to which the valve spring (or springs) is engaged.
A longstanding goal of engine design is to produce greater engine power while simultaneously achieving better fuel economy. Engine components of lighter weight further this goal because lower engine component weight decreases the amount of work necessary for operation, thereby increasing engine efficiency.